Nearest Note
A4
MIDI
69
Cents
+0.0
Nearest Note
A4
MIDI #
69
Cents
+0.0
Wavelength
0.78 m
| Note | Frequency | MIDI |
|---|---|---|
| E4 | 329.63 Hz | 64 |
| F4 | 349.23 Hz | 65 |
| F#4 | 369.99 Hz | 66 |
| G4 | 392.00 Hz | 67 |
| G#4 | 415.30 Hz | 68 |
| A4 | 440.00 Hz | 69 |
| A#4 | 466.16 Hz | 70 |
| B4 | 493.88 Hz | 71 |
| C5 | 523.25 Hz | 72 |
| C#5 | 554.37 Hz | 73 |
| D5 | 587.33 Hz | 74 |
Inputs
Result
n = 12 × log₂(440/440) + 69 = 12 × 0 + 69 = 69. MIDI 69 = A4. Cents = 0 (exact match). Wavelength = 343/440 = 0.78 m.
Inputs
Result
n = 12 × log₂(261.63/440) + 69 = 12 × (-0.75) + 69 = 60. MIDI 60 = C4 (middle C). Wavelength = 343/261.63 = 1.31 m.
Inputs
Result
n = 12 × log₂(80.5/440) + 69 ≈ 39.6, rounds to 40 = E2 (82.41 Hz). Cents = 1200 × log₂(80.5/82.41) ≈ -40.5 cents (significantly flat).
Use the formula n = 12 × log2(f / 440) + 69 to find the MIDI note number, then map to note names. For example, 261.63 Hz gives MIDI 60 = C4 (middle C). The cents deviation shows how far off the frequency is from the nearest note.
| Note | Frequency (Hz) | MIDI # | Common Use |
|---|---|---|---|
| C4 | 261.63 | 60 | Middle C |
| A4 | 440.00 | 69 | Tuning standard |
| E2 | 82.41 | 40 | Low E guitar string |
| C8 | 4186.01 | 108 | Highest piano note |
| A0 | 27.50 | 21 | Lowest piano note |
A4 = 440 Hz is the ISO 16 international standard pitch adopted in 1955. Some musicians prefer 432 Hz ("Verdi tuning"), claiming it sounds warmer or more natural. The difference is about 31.77 cents (roughly 1/3 of a semitone). Most modern instruments and digital tuners use 440 Hz.
| A4 Standard | Frequency | Middle C (C4) | Usage |
|---|---|---|---|
| Baroque | 415 Hz | 246.94 Hz | Period instruments |
| Verdi | 432 Hz | 256.87 Hz | Alternative tuning |
| ISO 16 | 440 Hz | 261.63 Hz | International standard |
| European | 442 Hz | 262.81 Hz | European orchestras |
Cents are a logarithmic unit for measuring musical intervals. One semitone = 100 cents, one octave = 1200 cents. Calculate cents between two frequencies: cents = 1200 × log2(f2 / f1). A trained ear can detect differences of about 5–10 cents.
| Interval | Cents | Frequency Ratio | Example |
|---|---|---|---|
| Unison | 0 | 1.000 | Same note |
| Semitone | 100 | 1.059 | C to C# |
| Whole Tone | 200 | 1.122 | C to D |
| Perfect Fifth | 700 | 1.498 | C to G |
| Octave | 1200 | 2.000 | C4 to C5 |
MIDI assigns numbers 0–127 to musical notes. Middle C (C4) is MIDI 60, A4 is MIDI 69. Each increment is one semitone. MIDI is used in all digital audio workstations, synthesizers, and electronic instruments for note communication.
Equal temperament divides the octave into 12 equal semitones, each with a frequency ratio of 2^(1/12) ≈ 1.05946. This means every semitone is exactly 100 cents. It is the most common tuning system in Western music, allowing free modulation between keys.
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Last Updated: Mar 25, 2026
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